1. Field of the Invention
The present invention relates to a data processing apparatus having a display device, and, more particularly, to a data processing apparatus for a multitask operation-multiwindow for use with a pointing device such as a mouse.
2. Related Background Art
In a multitask operation system such as UNIX or OS/2 ("UNIX" and "OS/2" respectively are trade marks of AT & T Bell Laboratories, U.S.A. and IBM, U.S.A.), tasks are simultaneously but asynchronously processed. For example, a plurality of tasks can be simultaneously processed even if the system is performing the control of the display thereof. Furthermore, a task can be transferred from a host to another host and the task can be executed in a group composed of a plurality of host computers mutually connected to each other via a network. In a multiwindow system, information about each task which is being executed is displayed simultaneously on each window of the screen. Among the multiwindow systems of the aforesaid type, X-window is a typical multiwindow system available at present ("X-window" is a trade mark of Massachusetts Institute of Technology).
Hitherto, a refresh scanning type CRT (Cathode Ray Tube) has been usually used as a display device for a computer terminal. A vector scanning type CRT has been frequently used as a large size precise display relating to the CAD (Computer Aided Design).
In the vector scanning type CRT, an image, which is once displayed, is maintained by the memory function until the next screen refreshment (refreshment of all of the screens) is performed. However, the vector scanning type CRT has not been suitable to serve as a real type man-machine interface display such as a moving cursor display, moving icon display, a pointing device such as a mouse or editor display because of its unsatisfactory operation speed.
On the other hand, the refresh scanning type CRT has no memory function and therefore a refresh cycle must be performed at a predetermined frame frequency, the refresh cycle enabling new screens to be supplied at each frame frequency. The aforesaid frequency is the inverse number of the product of the number of scanning lines per frame and the horizontal scanning time for each line. In order to prevent flicker, it is preferable that the aforesaid frequency be 60 Hz or more.
A non-interlace scanning method is commonly utilized in both of the aforesaid type CRTs, the non-interlace scanning method enabling the data movement display on the screen, for example, the icon movement display to be suitable to be observed and followed by a user.
Both of the aforesaid types of CRTs encounter problems in that the size of the display device becomes enlarged and electricity consumption becomes large in proportion to the required display resolution when the resolution is improved for the purpose of, for example, adequately displaying the multiwindow. What is worse, the cost of the drive circuit cannot be reduced. As described above, the large-size and high resolution CRT gives rise to a variety of problems. Therefore, a flat panel type display has been developed recently.
There are a variety of flat display panels including a type which employs the high multidrive system using super twist nematic liquid crystal (STN), and a type which is the modification of the aforesaid type and which has a white/black display, and another type which has a plasma display. All of a variety of the aforesaid flat display panels employ a CRT system image data transferring system and a non-interlace scanning system in which the screen refreshment is performed at a frequency of 60 Hz or higher. Therefore, an unsatisfactory number of 400 to 480 scanning lines can be poorly obtained for one full screen. For example, a large flat display panel having 1000 or more scanning lines has not been put into practical use. The reason for this lies in that satisfactory contrast cannot be obtained in the aforesaid large size flat display panel because the scanning time for one line becomes 10 to 50 .mu.sec or shorter due to performing the refresh cycle which must be carried out at a frame frequency of 60 Hz or more for the purpose of preventing flicker.
In the CRT, an image formed on the fluorescent screen is maintained for a certain time due to the fluorescent characteristics. In the TN type LCD (Twist Nematic type Liquid Crystal Device), an image is formed by utilizing change in the light permeability taken place due to an application of sufficient drive voltage. Both of the aforesaid types must use a high frame frequency which is higher than 30 Hz.
The horizontal scanning time of a CRT display or a TN type LCD having 1920 scanning lines, and 2560 pixels for a line, that is, 4,915,200 pixels for one frame becomes about 17.5 .mu.sec, while the horizontal dot clock frequency becomes about 147 MHz. In the case of the CRT, the horizontal dot clock frequency of 147 MHz is considerably higher than the maximum electron beam modulation frequency of a beam gun for use in a picture tube available at present. As a result, accurate image forming cannot be performed. In a case of the TN type LCD, the fact that 1920 scanning lines are driven comes under a duty factor of 1/1920 which is considerably lower than the minimum duty factor of about 1/400 at present. On the other hand, if driving at an actual horizontal scanning speed is used, its frame frequency becomes lower than 30 Hz and therefore flicker makes the display quality worse. Because of the aforesaid facts, the CRT and the TN type LCD present limits present in enlarging the size of the screen and making the screen precision finer due to the unsatisfactory number of the scanning lines.
Recently, Clerk and Lagerwall have disclosed a ferroelectric liquid crystal device (FLCD) having both high speed responsibility and memory characteristics (bistability) (U.S. Pat. No. 4,367,924). The FLCD has smectic C-phase (SmC*) or H-phase (SmH*) at the characteristic temperature thereof and becomes optically bistable state. Furthermore, the state of the FLCD is changed at high speed in accordance with the applied electric field. Therefore, there is a desire to widely use the FLCD as a display device having high speed memory characteristics.
There is a probability, by using the FLCD, of realizing a large and fine display device which is far superior to the above-mentioned flat panel display device. Since the FLCD must be driven at a relatively low frame frequency, its memory function is utilized so as to realize a partial rewriting scanning function for the purpose of making it an adequate man-machine interface display. The term "partial rewriting scanning function" used hereinbefore means a function that only a region on a screen to be rewritten is scanned and a new picture drawn in the aforesaid region. The partial rewriting scanning has been disclosed in U.S. Pat. No. 4,655,561. As a display using the bistable function of the FLCD, a flat panel (1920 scanning lines).times.(2560 pixels for a line) has been realized.
In the FLCD line scanning method, the frame refresh frequency is lowered in inverse proportion to the number of the scanning line. For example, the frame frequency of an FLCD the speed of which is 50 .mu.sec/line can be expressed by the following equation: EQU 1920 (lines).times.50 (.mu.sec/line)=96 (msec)=10 (Hz)
On the other hand, the movement of the pointing device, the real time responsibility of the data input by using the keyboard and smoothness of the same are important factors for the operationality of the computer. Although the pointing device index (for example, the mouse font) and the characters have relatively small size as compared with the size of the frame on the screen, high speed responsibility is required when they are displayed. For example, the mouse font and the characters must be usually treated at 60 Hz and 30 Hz, respectively. Therefore, the frame frequency of 10 Hz is insufficient to perform the aforesaid operations.
The aforesaid "partial rewriting scanning technology" is a technology in which a new picture is drawn to rewrite a former picture in a required region in the display, the "partial rewriting scanning technology" being effective to significantly shorten the time required to update the picture to be drawn. If the mouse font is formed with 32.times.32 bit data, the data display speed becomes as follows: EQU 32 (lines).times.50 (.mu.sec/line)=1.6 (msec)=625 (Hz)
When the "partial rewriting scanning technology" is actually used, a "partial rewriting command" must be recognized and the number of scanning lines to be rewritten must be indicated on the display. Because of other factors, the actual frequency at the time of the partial rewriting operation is about 300 Hz. If the partial rewriting operation is performed at about the aforesaid frequency, a significantly improved effect can be obtained in displaying the mouse font or the like on a large size display in a real time manner.
Then, a consideration will be made about a case in which a window system such as the X window is, in the UNIX environment, operated on the display which is arranged to use the aforesaid partial rewriting scanning technology. In the window system, the X-server detects an input made by a user through a pointing device such as a mouse (hereinafter the pointing device is represented by the "mouse") or a keyboard and the X server notifies it to an adequate client process in accordance with the X protocol. At this time, the conventional X server, as frequently as possible, examines the presence of the hardware event to quickly notify the result to the client process in such a manner that the aforesaid operation is periodically performed by a predetermined number of steps in the loop in the server. The aforesaid method is established depending upon an idea that the server must precisely notify the client the event and the treatment of it must be charged by the client, the method being utilized from an ordinary method employed in a conventional X server for the CRT display.
However, the conventional hardware event detection and notifying method encounters a problem in the response of the mouse operation with a graphic user interface using the mouse.
For example, FIG. 11 illustrates a case where a certain graphic object is being moved in response to mouse dragging. At this time, a so-called "direct operational" user interface is employed so as to always update the display of the object to a new position in accordance with the movement of the mouse.
FIG. 8 schematically illustrates the time sequential flow of the process from a moment at which a hardware (mouse) event takes place to a moment at which a picture is drawn on the display. Referring to FIG. 8, a generated mouse event is immediately stored in a hardware (H/W) event queue, and the mouse event is notified to a corresponding client process. The client process which has received the mouse event analyzes the H/W event so as to generate a picture draw request. The server of the window system, which has received it, processes the picture draw request issued from the client process, and then the server issues some picture draw commands to a remote processor (the graphic device processor). On the other hand, the remote processor processes the picture draw commands issued from the server to actually draw a picture on the display (draw a picture on a frame buffer).
However, if a time delay takes place at a step in a process from the generation of the event to drawing of a picture on the display, the time delay between the generation of the even and drawing the picture on the display is lengthened. For example, the time taken to process the final picture draw command cannot catch up with the command issue speed mainly due to the characteristics of the hardware. Furthermore, the CPU allocation time given to the aforesaid process can be shortened for some reason in the environment of the multitask. As a result, as shown in FIG. 8, a considerably long time difference takes place between the generation of the hardware event to the picture draw process performed by the graphic device processor. Consequently, the system of this type becomes a system, the real time characteristics of which are unsatisfactory, and which cannot be used easily for the operator of the mouse.
The aforesaid time delay must be improved by raising the hardware operation speed of the graphic device and by a software means such as the aforesaid partial rewriting scanning technology. The so-called "direct operational" user interface is expected to be widely used with recent rise of the importance of the recent graphic user interface. Therefore, it is very important to overcome the aforesaid problems.
In the operation of a computer, an input from the mouse or the keyboard is called a "hardware (H/W) event" which must be processed for the computer system in a real time manner as much as possible. The reason for this lies in that the H/W event directly relates to the operation performed by the operator and therefore the real time characteristics of the H/W event determines the operationality.